Spatially resolved transcriptomic profiling of placental development in dairy cow

The placenta plays a crucial role in the successful reproduction of mammals. Ruminant animals possess a semi-invasive placenta characterized by a highly vascularized structure and formed by maternal endometrial caruncles and fetal placental cotyledons. This specialized placenta is essential for fetal development until full term. The cow placenta consists of at least two trophoblast cell populations, including uninucleate (UNC) and binucleate (BNC) cells. However, the current inability to describe the transcriptomic dynamics of the placental natural environment has resulted in a poor understanding of the molecular and cellular interactions between trophoblast cells and niches, as well as of the molecular mechanisms controlling trophoblast differentiation and functionalization. To fill in this knowledge gap, we employed Stereo-seq, a spatial transcriptomics technique, to generate a map capturing the spatial gene expression patterns at near single-cell resolution in the cow placenta on 90 and 130 days of gestation, and attained high-resolution, spatially resolved gene expression profiles of cow placenta. Based on clustering and cell marker gene expression, key transcription factors, including YBX1 and NPAS2, were revealed to regulate the heterogeneity of trophoblast cell subpopulations. Cell communication and trajectory analysis provided a framework for understanding cell-cell interactions and the differentiation of trophoblasts into BNCs in the microenvironment of the cow placenta. Differential analysis of cell trajectories identified a set of genes involved in regulation of trophoblast differentiation. Additionally, we identified spatial modules and co-variant genes that play critical roles in shaping specific tissue structures. Together, this foundational information contributes to the discovery of important biological pathways underlying the development and function of the cow placenta.